Fast Water Transport through Subnanometer Diameter Vertically Aligned Carbon Nanotube Membranes

Small-diameter carbon nanotubes (CNTs)have outstanding mass-transportproperties, especially enhanced water flow. Here, we report on watertransport through the first macroscopic membranes with verticallyoriented, subnanometer (0.8 nm) CNT pores, made by a scalable, solution-basedmethod with electric-field alignment of bulk-grown single-wall CNTs(SWCNTs). After plasma etching to open pores, vertically aligned CNTsserved as the primary pathway for liquid-water transport. The CNTmembranes showed fast pressure-driven water transport, with up to10(5)-fold enhancement compared to no-slip Hagen-Poiseuilleflow. Comparing 0.8 and 3 nm CNTs, we found that the hydrodynamicslip lengths increased with decreasing nanotube diameter, reaching8.5 mu m for the smaller-diameter CNTs. The results suggest thatpressure-driven water transport in small-diameter CNTs is increasinglydominated by entrance resistance, thus becoming independent of nanotubelength. Scalably fabricated membranes incorporating vertically alignedsubnanometer CNT pores could have applications in water filtration,desalination, and energy harvesting.